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A new review paper in Nature makes a stab an answering the question “Has the Earth’s sixth mass extinction already arrived?” In an apparent effort to satisfy a variety of audiences with different evidentiary and skepticism standards, Nature and the reviews authors, led by Anthony D. Barnosky of the University of California, Berkeley, offer a variety of phrasings.

First we have the paper’s abstract, which wraps up with:

Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.

Then we have this from further down (behind the paywall):

Although there are many definitions of mass extinction and gradations of extinction intensity, here we take a conservative approach to assessing the seriousness of the ongoing extinction crisis, by setting a high bar for recognizing mass extinction, that is, the extreme diversity loss that characterized the very unusual Big Five (Table 1). We find that the Earth could reach that extreme within just a few centuries if current threats to many species are not alleviated.

The journal’s editors present this summary:

Palaeontologists recognize five major extinction events from the fossil record, with the most recent, the Cretaceous mass extinction, ending some 65 million years ago. Given the many species known to have disappeared in the past few thousand years, some biologists suggest that a sixth such event is now under way. Barnosky et al. set out to review the evidence for that claim, and conclude that the recent loss of species is dramatic and serious, but not yet in the mass extinction category — usually defined as a loss of at least 75% of Earth’s species in a geologically short time frame. But that said, there are clear indications that the loss of species now classed as ‘critically endangered’ would soon propel the world into its sixth mass extinction.

If endangered species continue to disappear, we will indeed experience a sixth extinction, over just the next few centuries or millennia.

The Berkeley scientists warn that their new study may actually grossly underestimate how many species could disappear

Zimmer then launches into a comprehensive exploration of the question of whether or not we can blame these looming extinctions on global warming. Opinions are divided on the cause, we learn, although there is a consensus that we’re losing biodiversity. There’s also the reality that some species will be able to adapt to whatever changes are in store for the climate, while others will be replaced.

For me, the take-home message is change is inevitable. One can argue that change in of ifself is neutral. Could be good, could be bad. Depends on what kind of change you’re talking about. But given 1) how dependent the human species is on the way the ecosystem works now — think of the hundreds of millions of people who rely on protien from the ocean, for example — and 2) how long it takes ecosystems to restore their productivity levels, rapid and extensive change is unlikely to be good for us. It would be foolish to assume that the consequences will be anything but consequential.

The Climate Change mistake wasnât climate change, it was climate CONTROL and was a CO2 death threat to billions of children from unstoppable warming and nothing more. You canât have a little crisis.

If the heartless fear mongers had really loved the planet they would have been happy unstoppable warming was grossly exaggerated and therefore mankindâs worst crisis ever, was thankfully averted. Fear is always unsustainable.
As for you criminals in the media and you lab coat consultants? :History is noting that Scientists and journalists have done to science and journalism what abusive priests did for religion.
American IPCC funding is gone and Obama didnât even mention the CRISIS in his state of the union address and there is real talk now for criminal treason charges being laid against those in academia responsible for leading us to a false war against climate variation. And meanwhile, the UN had allowed carbon trading to trump 3rd world fresh water relief, starvation rescue and 3rd world education for just over 24 years of climate control instead of needed population control. History is watching.

@minimind
As at today the sea-ice total for both the Arctic and Antarctic is one and a half million square kilometers below the 1979-2008 mean. As I doubt that you would recognise a square kilometer if it up and bit you, that can be visualised as area of about one sixth of the United States.
Make no mistake, global warming is real and, if you don’t want to be cursed by your children or your children’s children, you should do something about it.
Oh, and overpopulation is a cause of global warming. That also needs to be addressed.

Zimmer then launches into a comprehensive exploration of the question of whether or not we can blame these looming extinctions on global warming

Oh, of all the self-blinded and mono-causalistic things for an otherwise smart person to say!

The environmental movement has got to stop reading global warming into every other environmental problem, because as in this case the result is to delegitimize those problems and make us lose sight of the actual causes and effects. We should only WISH that global warming were the cause of the biodiversity crisis. It would be a mercy. It would be a cause for celebration. I’d buy a freaking cake.

Because you see, wild systems have SOME chance–some plausible potential–of being able to adapt to wobbling temperature extremes that manifest over the next 100-200 years. But instead, the biodiversity crisis is almost exclusively caused by habitat destruction, with a major secondary cause being direct overexploitation. And that doesn’t take a lifetime. You can wipe out a population of large land vertebrates in one or two years. You can slash, burn, and poison an ecosystem in A WEEK. And we have, and we are, which is why this problem exists.

Quit it with the mono-causalism, guys. Wildlife conservation is a lot more practically and politically achievable than everything that has been tried so far for global warming, yet it has been all but removed from the conversation because AGW seems to be the only issue that mainstream environmental / progressive groups talk about anymore.